In recent years, from the viewpoint of miniaturization of machines and high printing speeds, there has been widely used a toner containing a polyester excellent-in the low-temperature fixing ability as a main component of the resin binder. Generally, the low-temperature fixing ability is improved by lowering the softening point of the resin. However, a resin having a low softening point is likely to generate offset during fixing by a heat roller fixing method. As a countermeasure for this disadvantage, there has been known a toner containing a resin binder of a combination of a low-softening point polyester and a high-softening point polyester (see Japanese Patent Laid-Open No. 2003-119351).
However, in general, resins having a low softening point have a low melt viscosity, so that homogeneous dispersion of various additives, in particular, magnetic powder, is not easily achieved, whereby triboelectric stability is insufficient. Even when such a resin is used together with a resin having a high softening point, satisfactory results have not been obtained.
On the other hand, as a means of improving dispersibility of an additive such as a magnetic powder, there have been known, for instance, a toner containing a polyester having a specified hydroxyl value and a magnetic material to which a carbon black is adsorbed on its surface (see Japanese Patent Laid-Open No. 2001-296689); a toner containing fine magnetic particles treated with a titanate coupling agent (see Japanese Patent Laid-Open No. Hei 4-124681); a toner containing a polyester obtained from specified raw material monomers and a magnetic material (see Japanese Patent Laid-Open No. Hei 5-134454); and the like. However, further improvement has been desired for satisfying both low-temperature fixing ability and triboelectric stability.